Measure the futon's dimensions, including the seat top, seat bottom, backrest, rear backrest, and taking note of the armrests if necessary to determine the amount of fabric required. Add a full yard of fabric to the final number to account for any extra problems or difficulty during the fabric installation.
Stretch the fabric over the backrest of the futon and over the seat and armrests. Tuck the fabric into the corners and edges of the seat.
Stretch the fabric tightly and pin the fabric, in the corners and edges of the seat, to the fabric on the other layer of the frame, using 1/2-inch safety pins. Pin all the way around the seat to keep the fabric in place when the futon reclines. Tuck the remaining fabric under the futon and pin it together securely with the safety pins.
Determine the length and width of the seat, armrests, backrest and rear of the couch, using a tape measure. Multiply each set of values together to find the area of each section, then add the areas together to find the total area. Add one yard to the total area to make the installation easier, and account for variances, and cut out this amount of fabric.
Drape the fabric over the seat of the futon and use the carpentry stapler to staple the fabric to the wood frame, stretching the fabric tight and stapling every six inches, pulling the extra front fabric under the futon. Spread the fabric up and over the backrest and staple it tight on the rear of the backrest, every six inches along the edges of the backrest, pulling the rest of the fabric under the futon. Stretch the fabric over the armrests and pull it under the futon.
Flip the futon upside down and pull the fabric tight all along the edge. Staple it to the bottom of the futon about three inches from the outside border, with staples every four inches along the border. Cut off any excess fabric with scissors right at the staple line.